Today, civil engineers make a deal with the Devil.
The University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.

We recycle most of our
drinking water. We've used it before, and we must
clean it before we use it again. We recycled water
without cleaning it a hundred years ago. So typhoid
and cholera were rampant. Then we added chlorine to
city water systems. It worked. Typhoid and cholera
are almost unknown in America today.

Then, in 1950, a new problem surfaced. Industries
were dumping a lot of organic chemical waste into
water systems. We were rid of germs. Now we had to
get rid of those chemicals.

First we needed new techniques of chemical analysis
to find out what was there. In 1974 two chemists
solved the problem in different ways. A Dutchman,
Johannas Rook, came out of the brewery business. He
simply capped off a partially filled bottle of
water and waited. Then he tested the air above it.
That's the same way you find contaminants in beer.

The other chemist was Thomas Bellar with the EPA,
an expert in air pollution. He bubbled clean air
through the water. The contaminants were absorbed
into the air, and he measured them. Rook and Bellar
each obeyed the first principle of invention. Each
brought alien expertise to the problem.

Then a bomb fell. Both Rook and Bellar made the
same horrifying discovery. More chemical pollutants
came out of the chlorinated water than went into
it. Chlorine reacts to create new carcinogens. The
worst of these is chloroform.

So we were rid of cholera at the cost of cancer.
The government responded by putting a legal limit
of 100 parts per billion on chloroform in our
drinking water. That's still enough to cause one
extra cancer death in 10,000 people who drink the
water all their lives. The trouble is, we pay a
price for getting even that low. We have to cut
back on our use of chlorine until we're once more
at some risk of water-borne disease.

By the way, you might wonder about fluoride. After
all, it's a chemical cousin to chlorine. Fluoride
is pretty nice stuff. Unlike chlorine, it doesn't
react to produce anything nasty. And it's not a
carcinogen itself. The traces of fluoride we put
into water really do drastically cut tooth decay.

Chlorine is another matter. It tells the tale of
our technology-dense world in microcosm. We trade a
few deaths to avoid many. That's a not a deal we
can accept in the long run. Since 1974 we've fought
it. We've brought millions of dollars to bear on
the problem. We haven't beaten it yet, but we will.
Because, after all, solving that kind of problem is
what engineering is all about.

I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.

See also a handbook on halogen treatment of
drinking water prepared by a group of leading
environmental engineers:

Treatment Techniques for Controlling
Trihalomethanes in Drinking Water. American
Water Works Association, 1982.

Our water in Houston contains less than the
mandated limit of chloroform -- 100 parts per
billion. That leaves us at somewhat greater risk
from pathogenic microbes, although we meet
government standards there as well.

Some cities violate the standards and let
chloroform run to 300 ppb. That assures safety from
pathogenic microbes. But it also threatens three
cancer deaths in every 10,000 people.

Of course, these numbers are trivial in comparison
with other carcinogens. We accept vastly greater
damage from tobacco. Even second-hand smoke
inflicts far more cancer than drinking water ever
does.